The present invention generally relates to an organic light-emitting diode display panel, and more particularly, to an organic light-emitting diode display panel that compensates for variations in threshold voltages.
At present, small, thin, short, and light-weighted electronic products are popular and easily accepted by consumers. Also, because of the advantages of being light, thin and easy to place and carry in comparison with the traditional cathode ray tube (CRT) displays, flat panel displays have become widely used nowadays and have a bright prospect.
Please refer to FIG. 1, which illustrates a conventional voltage-driven organic light-emitting pixel 100, the voltage-driven organic light-emitting diode pixel 100 includes transistors m1, m2, m4, m5, m6, and a capacitor Cst having terminals C and D. In addition, a sustaining voltage line Sus_N−3 is electrically coupled to the transistor m5, a scan line Scan_N−3 is electrically coupled to gates of the transistors m2, m4, m5, and m6, and a data line Data_N−3 is electrically coupled to the transistor m6. The signal carried on the scan line Scan_N−3 can determine whether to establish a connection between the terminal C and the sustaining voltage line Sus_N−3 or between the terminal C and the data line Data_N−3. A terminal of the transistor m1 is electrically coupled to a first predetermined voltage VDD. Furthermore, a terminal of the transistor m4 is electrically coupled to a terminal of an organic light-emitting diode 110, and another terminal of the organic light-emitting diode 110 is electrically coupled to a second predetermined voltage VSS. The above-mentioned circuitry structure can compensate for variations in the threshold voltages (Vth) of the driving transistors of the voltage-driven organic light-emitting pixels. To realize such a compensation function, a prerequisite is that the circuit has to ensure that a voltage of the capacitor terminal D is pulled down to a voltage less than VDD−Vth before data is written; otherwise the compensation function of the pixel circuit may fail. However, this circuitry structure does not provide such an assurance action; the pixel circuit therefore has a low stability, and this may lead to luminance non-uniformity (so-called “Mura”) of the display panel due to failure of the compensation function.
FIG. 2 illustrates a timing diagram of signals of the pixel circuit of FIG. 1. Referring to FIGS. 1 and 2, the data line Data_N−3 carries a data signal voltage Vdata0 of a data signal Data0. The scan line Scan_N−3 carries a scan voltage signal VScan_N, and the sustaining voltage line Sus_N−3 carries a sustaining voltage Vsus. At image 0, the scan voltage signal VScan_N is at “LOW” logic level, the data signal voltage Vdata0 of the data signal Data0 on the data line Data_N−3 is written into the terminal C and the voltage of the terminal D is pulled up to VDD−Vth. Then, when the scan voltage signal VScan_N is at “HIGH” logic level, the voltage of the terminal C is pulled up by a voltage difference of (Vsus−Vdata0). At this time, the voltage of the terminal D is pulled up to VDD−Vth+(Vsus−Vdata0) due to the voltage stabilization effect of the capacitor Cst. Thereafter, the operation at image 1 is similar to the operation at image 0, but it can be seen from FIG. 2, before the data signal Data l is written into the terminal C, the situation of Vd>VDD−Vth is still not improved. As a result, the panel formed by the voltage-driven organic light-emitting diode pixels is not able to compensate the threshold voltage (Vth) variation of the driving transistors of the voltage-driven organic light-emitting diode pixels.
In another aspect, current flat panel displays are becoming higher in resolution. The traditional pixels may not be suitable for use in active organic light-emitting diode display panels with high resolution. This is because the pixels include too many transistors, causing the aperture ratio to be too low.